Alkylidene Meldrum's Acids as Platforms for the Vinylogous Synthesis of Dihydropyranones

Abstract

Upon Brønsted base organocatalysis, ketone-derived alkylidene Meldrums acids proved to be competent vinylogous platforms able to undergo a formal (4 + 2) cycloaddition reaction with dihydro-2,3-furandione, providing an unprecedented route to 3,6-dihydropyran-2-ones as spiro[4.5]decane derivatives with up to 98 % ee thanks to the commercially available Takemoto catalyst. Preliminary investigation showed that this reaction could be extended to other activated ketones, establishing these alkylidene Meldrums acids as a novel C4synthon in the vinylogous series.Scheme 1. Novel organocatalytic vinylogous synthesis of dihydropyran-2-ones.

Alkylidene Meldrum′s Acid as Acceptor‐Donor‐Acceptor with Azomethine Ylide for Organocatalytic Asymmetric (3+2) Cycloaddition/Annulation: Synthesis of Chromeno[4,3‐b]pyrrolidine

“…Hence, in continuation of our research interest in developing efficient enantioselective synthesis of chromenopyrrolidines and exploring the chemistry of AMAs as acceptor‐donor‐acceptors in double annulation reactions, [7e,f] we envisioned utilizing the structural specialty and high reactivity of AMA to accomplish this goal [2g,8] . Moreover, we expect the non‐planar structure of Meldrum′s acid moiety would assist the catalyst in differentiating the facial selectivity and thus enhance the stereoselectivity of the reaction.…”